Six people who underwent heart surgery at an Edinburgh hospital contracted infections related to mould, the Scottish Health Secretary said.
Jeane Freeman told MSPs at Holyrood that three different types of mould infection had been identified in the patients - who all had cardiothoracic surgery at Edinburgh Royal Infirmary - with "some" of those affected having died.
Health Protection Scotland advised on February 19 that one patient who had undergone the procedure had contracted a mould infection, Ms Freeman said.
A month later, on March 19, bosses at NHS Lothian wrote to 186 people who had undergone the procedure to warn them of a "low infection risk arising from their surgery".
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Ms Freeman said that none of the types of mould involved were "commonly found in hospitals".
She confirmed: "Three types of mould infection have been identified which have affected six patients.
"Sadly some of those six patients have died."
With the news coming in the wake of infection-related deaths at the £842 million Queen Elizabeth University Hospital in Glasgow, opposition MSPs said confidence in the NHS had slumped.
Scottish Conservative health spokesman Miles Briggs told the Health Secretary: "It is quite clear public confidence has been shattered recently in our NHS estate."
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Scottish Labour's Monica Lennon said: "Unfortunately, here we are again. It's a different hospital, a different city, different infections, but the outcome is the same - patients have died and public confidence continues to dip."
NHS Lothian ordered "specialised cleaning and environmental decontamination with hydrogen peroxide vapour" in relevant wards and theatres of the hospital after the infections were discovered, Ms Freeman said.
She said the source of the infections had yet to be identifed.
"Once we have identified the source there will be lessons to be learned from that," she added.
"Healthcare associated infection outbreaks are rare and whilst it is important to respond when they do occur... they do affect a very small proportion of the 1.2 million in-patient and day cases treated every year in Scotland."
The Health Secretary added: "Not all healthcare associated infections are preventable.
"But we do have dedicated professionals and a rigorous system focused on limiting them and controlling them."
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